I would like the ability for the person assigned a task to put in how many hours it took to complete the task. It would simplify my billing. I don't need anything fancier than total hours and minutes spent, but some day to add date and time spent would be awesome too.

There are a thousand reasons why people want to add a post-hoc category. Being able to see all items with that category provides sorting power. Personally I use Covey's Four Quadrants system for various management applications. Being able to tag Q1-Q4 for example would enable me to use Manage It to implement this strategy

Add the option to change colors on projects and tasks within (maybe a choice of 10 colors). With a marketing plan with multiple tasks assigned to different people, different colors is a must to make it clear to see on a calendar. Please add this!

We used a couple of ManageItApp projects to put on our dog shows this past year, Now the cycle starts again and it would be great to be able to copy the projects from last year, including the tasks and subtasks (have them not marked as completed of course). Then I'd have all the tasks that need to be done, I'd just have to adjust dates...

Currently, you post the task and set a due date! There are often several actions that need to happen from start to finish. Having just the due date without the ability to set "Next Action" within a task, with a day, date, time reminder makes the app less effective. This "next step" is common in CRM apps to notify user when to make the next call to a prospective customer

Along with the ability to email a task, to send a task or sub-task via text to a specific person or group without assigning the person or group will be an effective way to save time & increase efficiency.

I have tested a lot of these type of apps lately and this is the simplest I have used, I love it. I would like to tie it one with my other apps and even wordpress.
All my business applications are web based and have API access. Even connection via zappier would be useful.
Thanks